In the study of the human filariases, progress has been hampered by 1) the lack of defined parasite antigens; 2) the broad immunological cross- reactivity seen among the eight filarial species of humans; and 3) the dearth of abundant parasite material. The objectives of this project are to define and generate filarial proteins that are important in inducing parasite-specific immune responses in the human host and to understand, at a molecular level, the differences among related filarial species. cDNA and genomic libraries have been either constructed (Brugia malayi, Loa and Wuchereria bancrofti, Onchocerca volvulus) or made available (Onchocerca volvulus, Brugia malayi larval cDNA library) so that screening with defined patient sera, patient T cells or parasite DNA could be performed. Recombinant antigens and probes have been identified that a) induce T cell responses in an antigen-specific manner, b) may be in part protective in onchocerciasis; c) can distinguish among related filarial species by restriction fragment length polymorphisms, PCR or direct Southern blotting; d) encode immunoreactive and potentially protective molecules of W. bancrofti; e) identify repeated segments of either the W. bancrofti genome or that of Loa; and f) may be of potential diagnostic importance.